1. lck processes to pick up extra or missed 'posts' (messages).
in all cases that can be identified the wait time is zero,
although on most ports this is changed to 1/100th second in
order to force the process to be rescheduled.

2. multiple db writers.

two cases:

- when the master has sent i/o requests to the slaves, it
waits on this event for up to 6 seconds until the slaves
signal that the i/o is complete.

- the slaves wait on this event for up to 3 seconds whilst
waiting for requests from the master db writer.